1. Field of the Invention
The invention relates to a method for processing fish by deboning, which fish are conveyed with their head leading and from which meat is obtained by detaching and removing the belly and back spokes of the fish as well as the ribs and the vertebral column. The invention also relates to an apparatus for performing such method, the apparatus comprising a conveyor for advancing the fish with their head end leading as well as tools for cutting free the belly spokes and the ribs up to the back spokes.
2. Prior Art
Due to the progressing shortage and rise in price of fish as well as due to the simultaneously increasing demand for fish, it is of increasing importance in the processing of fish that fish to be processed are treated in a manner that the loss in fish meat appropriate for human nutrition is kept at a minimum. In the past, several concepts have been followed which were additionally based on this aspect.
For example, from German Patent 503 060 and the corresponding German Patent of Addition 509 733, there is known an apparatus for cutting open, cleaning and deboning fish. In this apparatus, a supporting disc driven to rotate is used as conveying means, which disc seizes the fish to pull them by their tail and support them by their backs. The deboning is performed by cutting free the flanks of the backbone or vertebral column by means of knife blades which are moved under control into the fish at both sides of the backbone. These blades have triangular shape and a forwardly projecting tip and slide underneath the rib bones in the manner of a wedge in the region of the belly cavity to scrape out these ribs from the belly wall. Thereafter, the deboning is completed by a tool which is formed by a pair of circular knives which are arranged in a roof-shaped manner with regard to each other and cut over the backbone to detach the same from the fish.
According to the patent of addition, a toothed disc is provided instead of the tool comprising the roof-shaped arranged circular knives, which toothed disc is formed by a pair of spaced toothed rings having teeth which project above the hub body of the toothed disc and are provided with peripheral cutting edges. A knife is arranged fixedly in the plane of rotation of the tips of the teeth. The width of this knife corresponds to the spacing of the toothed rings, while the leading portion of the knife is sharpened. It is the task of this knife to cut through the backbone at the tail root (FIG. 4 of DE 509 733) and to lift the backbone in the course of the further conveying, whereupon it may be taken out from the meat by the toothed disc.
Following the statements in the mentioned documents, the known apparatus is to be used, in general, in the processing of fish, particularly herrings. The expert, however, will recognise that this method can only be used for herrings or fish of the herring species due to the specific anatomic facts, the pulling conveyance by means of a tail clamp being a decisive prerequisite. The result does, by no means, meet today's demands in the product quality which, when the known method is used, is unsatisfactory insofar as the severing of the fish meat occurs only in the region of the teeth of the toothed disc which has the effect that when the backbone is lifted out the non-severed meat portions must be severed by tearing. The consequence of such action is that the fillets have a very rough surface in the back region, which cannot be accepted. On the other hand, the partial separation produced by the teeth has the effect that the connection between the flank portions of the fillet meat and the central meat strip containing the back spokes is weakened such that this meat strip is lifted out together with the back spokes when the backbone is lifted so that these meat portions are lost. This result also occurs due to the effect of the knife which separates the meat portions containing the back spokes as can be taken from FIG. 5.